Development in the field of teeth whitening has led to the presently used method of "power bleaching," which is generally described as follows. A rubber sheet or dam is placed over the patient's teeth so that the teeth protrude through the sheet. The dam is made from latex rubber forced over each tooth and held in place with metal springs, clamps, and ligatures. This partially protects the soft tissues of the gums from the peroxides used in bleaching. However, since the rubber sheet stretches and does not custom fit the particular patient's mouth, the peroxide can leak around the rubber sheet and cause substantial discomfort to the patient. Typically, this method can be performed only on the upper or lower set of teeth at a time, not both.
Once the rubber sheet is in place, a peroxide solution is coated on the teeth. Since the bleaching effects of peroxide are slow, the common practice is to apply heat to the peroxide to accelerate the reaction. This is accomplished with the use of a heat lamp or heating iron. Although the heat accelerates the bleaching process, a substantial amount of time is still required so that the entire bleaching process must be performed over several appointments, resulting in inconvenience, time loss, and substantial expense.
The heat lamp activates the peroxide on a plurality of teeth simultaneously but, due to the amount of heat required where heat is the sole means for activating the peroxide, also exposes the patient's face to significant amounts of heat, which is quite uncomfortable and cannot be endured for a prolonged period. While the heating iron does not expose the patient's face to the same extent as the heat lamp, it takes a much longer time to perform the whitening since it affects only one or two teeth at a time. In addition, prolonged exposure to heat will increase the temperature of the pulp within the tooth, causing discomfort to the patient if the pulp temperature gets too high. Since the amount of heat commonly used in this type of procedure could kill the pulp and cause tooth loss if exposure is prolonged, continuous exposure must be limited. As a result, 2 to 5 office visits are required before adequate bleaching is attained.
Other prior art tooth bleaching techniques utilize both light and chemical activation of hydrogen peroxide to accelerate the bleaching process. For example, in Toh, C. G. "Clinical Evaluation of a Dual-activated Bleaching System," Asian Journal of Aesthetic Dentistry, Vol.1, No. 2, pp. 65-70 (July 1993), a powder containing potassium persulphinate (sold under the name "Oxone" by the DuPont Corp.) was mixed with solutions of hydrogen peroxide to form a paste. The paste was applied to discolored teeth and activated using a dental curing light. Two different concentrations of hydrogen peroxide were used--19% and 35%. A similar process is disclosed in U.S. Pat. No. 5,032,178, which also mentions the use of a 30-35i% aqueous solution of hydrogen peroxide, with Oxone as an accelerator, and a dental curing light.
The described use of the laser whitening method of the present invention has certain advantages over the use of dental curing lamps and the like. For example, heat lamps designed for tooth whitening, such as the Union Broach Illuminator, utilize halogen bulbs which are significant sources of yellow light. However, because the pulp tissue in living teeth is red, it rapidly absorbs the yellow light causing it to rise in temperature, resulting in patient discomfort. A similar problem arises with incandescent bulbs. Like halogen bulbs, they produce all wavelengths of visible light, much of which is absorbed by the tooth pulp.
Also known in the art is the use of a laser in combination with hydrogen peroxide to bleach teeth. For example, Spanish patent application no. ES 528007, in the name of Vicente M. Torres Zaragoza, generally discloses the use of laser radiation to accelerate the bleaching action of hydrogen peroxide, but does not disclose a specific type of laser or method of using a laser to accelerate bleaching. Unlike curing lights, lasers permit the practitioner to expose selected teeth to a focused beam of light, thereby concentrating the energy of the beam where it is needed.
From the foregoing it may be seen that there remains a need for a method of whitening teeth which better protects the soft tissues, shortens the time for the procedure, and reduces the discomfort to the patient.
In accordance with the principles of the present invention, the use of the light source of the described laser permits the practitioner to choose the specific wavelength of such light that will be most effective in eliminating the particular stain. It is advantageous to select a wavelength close to the color of the stain to be bleached so that the light will be absorbed primarily by the stain molecules rather than the tooth pulp.